The Dow industrials on Monday were trading lower, weighed by a decline in insurer component Travelers Cos., as investors gauged the effect of Hurricane Harvey that slammed into Texas over the weekend, flooding cities and forcing energy facilities to close.

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The Dow Jones Industrial Average declined 19 points, or less than 0.1%, to 21,795. Insurance company Travelers Cos. Inc. (TRV) led losses, down 2.6%, and Goldman Sachs Group Inc.(GS) shares fell 1.3%. Home Depot Inc. (HD) and Apple Inc. (AAPL) were leading gainers, up 1.2% and 0.9%, respectively.

The S&P 500 index, which traded off between slight gains and losses, was last down 1 point at 2,442, with nine of the main sectors trading lower, led by a 0.9% decline in energy stocks and a 0.7% fall in financials. Health-care stocks were among the few gainers with a 0.7% advance.

Meanwhile, the Nasdaq Composite Index added 11 points, or 0.2%, at 6,276, driven by gains in technology and biotech names.

"Health care shares were up because of merger deals, but insurance companies are suffering because it's clear that the flooding damage in Texas will mean a lot of claims for payouts. It is unclear if a jump in gasoline prices is long-lasting because we don't know how soon refineries will be up and running," Mark Kepner, managing director of sales and trading at Themis Trading.

Kepner also said low volumes tend to exaggerate price swings on Wall Street.

At last check, 1.23 billion shares changed hands on the New York Stock Exchange by midday, with 827 million trading on the Nasdaq. Trading volumes were especially light last week, coming in below already seasonally low August averages. Daily average trading volume in August for the NYSE stands at 3.09 billion shares and 1.79 billion shares for the Nasdaq, according to Dow Jones data.

"Unless we hit some macro[economic] issues, we're in a little bit of a lull," said Diane Jaffee, senior portfolio manager at TCW, in an interview. "Earnings are still lending strength to the overall tone of the market, and people were thinking something would come out of Jackson Hole but nothing happened, so it's business as usual."

Jaffee said attention is more focused on company specifics, companies like Gilead Sciences Inc.(GILD) right now, rather than on macro issues. Although, if disappointing employment figures are released by Labor Department on Friday, that is likely to boost trading volume in a negative way, she said.

Read:Like Amazon, these 7 stocks have dropped 10% or more in a month--and analysts say buy them too (http://www.marketwatch.com/story/like-amazon-these-7-stocks-have-dropped-10-or-more-in-a-month-and-analysts-say-buy-them-too-2017-08-28)

Now-Tropical Storm Harvey devastated Houston, the fourth-largest city in the U.S., leaving its citizens grappling with unprecedented flooding. The National Weather Service warned that rainfall may exceed a record-breaking 50 inches in areas around Houston. (http://www.marketwatch.com/story/houston-forecast-unprecedented-50-inches-of-rain-2017-08-27)

The storm, which was moving toward Louisiana early Monday, knocked out almost 15% of the nation's fuel-making capacity and further disruptions were anticipated. The coast of Texas hosts nearly 30% of U.S. refining capacity, and Houston-area plants account for roughly half of that.

That led to U.S. gasoline futures jumping on Monday. On the New York Mercantile Exchange September futures recently traded 3.4% higher at $1.72 a gallon, and the more active October contract climbed 2.2%.

However, oil prices continued to decline. West Texas Intermediate oil futures fell 3.2% to $46.33 a barrel. The most popular ETF tracking oil prices, United States Oil Fund,(USO), slumped 3.1%.

Shares of energy companies (http://www.marketwatch.com/story/energy-stocks-try-to-shake-off-hurricane-harvey-fallout-with-dow-set-to-rise-modestly-2017-08-28) were also falling, as some major companies closed down refineries in Texas due to flooding. The SPDR Energy Select Sector exchange-traded fund (XLE) fell 0.7%.

Exxon Mobil Corp. (XOM) shut its Baytown refinery--the second largest in the U.S.--in a Houston suburb because of the heavy floodwaters, and Royal Dutch Shell PLC (RDSB.LN) said it stopped making fuel at its Deer Park, Texas, plant. Exxon shares fell 0.4%, while Chevron Corp. (CVX) shares were also down 0.7%.

"Although the full impact of the storm's damage is yet to be determined, the markets expect the impact will be felt globally and affect energy markets for many weeks," analysts at FxPro said Monday. "Following Hurricane Katrina in 2005, U.S. economic growth dropped by 50% in a quarter, therefore markets will be closely watching the damage from Harvey and its effect on the U.S. economy."

Economic data: The Commerce Department's report showed that the advanced trade gap in goods--services are excluded--widened by 1.8% to $ 65.1 billion in July (http://www.marketwatch.com/story/us-trade-deficit-widens-in-july-advance-report-shows-2017-08-28). Both exports and imports declined, but exports dropped at a faster pace in the month. The gap was wider than expected.

Corporates: Shares of Expedia Inc.(EXPE) fell 4.3% after news that Chief Executive Dara Khosrowshahi is leaving the company to become Uber's CEO (http://www.marketwatch.com/story/uber-said-to-pick-expedias-dara-khosrowshahi-as-new-ceo-2017-08-27).

Read: These 15 energy stocks are down more than 3.5% in the wake of Hurricane Harvey (http://www.marketwatch.com/story/these-15-energy-stocks-are-down-more-than-35-in-the-wake-of-hurricane-harvey-2017-08-28)

The ICE Dollar Index was down 0.6% to 92.22 as the greenback lost ground against the yen, the euro and pound.

In Asia, Hong Kong's Hang Seng Index edged up 0.1% while the Japan's Nikkei Average ended fractionally lower. European equities (http://www.marketwatch.com/story/european-stocks-under-pressure-as-euro-hits-highest-since-january-2015-2017-08-28) closed lower as the euro hit its highest against the dollar in more than two years.